Here's a scene from your two cities, Bill: In July 1985, Mark Campbell, 26, was charged with second-degree murder for delivering a fatal karate chop to his girlfriend's 17-month-old son — because the baby's crying kept him awake. Neil Schneider/NY Post

The New York Times is doing the city a favor. An editorial Monday declared that New Yorkers need not worry about a return of the violence that ravaged Gotham in the pre-Bloomberg/Giuliani days. In so doing, the paper crystallized the competing messages of this vital election year.

On one side are those who believe there’s nothing inevitable about the historically low crime levels New York enjoys today. This side believes that safe streets are the fruit of tough decisions taken by Mayors Giuliani and Bloomberg, and innovative tactics under Police Commissioners Bill Bratton and now Ray Kelly. This is the side of The Post, the police and mayoral candidate Joe Lhota.

On the other side are those who pretend we’ve solved this problem forever and the ugliness can never return. This side includes the Times and the man it seems likely to endorse for mayor, Bill “Tale of Two Cities” de Blasio.

Fact is, what we have here is a tale of two New Yorks. But two cities we should be comparing are these: the pre-Giuliani, bullet-riddled New York that had 2,245 murders in 1990, and the New York we have today, where 417 were killed last year.

All that seems lost in the Times’ headline, “Don’t Fear the Squeegee Man.” It is meant to be mocking, but it is highly revealing, for here we have the liberal zeitgeist in full flower. In an editorial focused on policing, Commissioner Kelly — the most successful police commissioner in the United States — goes completely unmentioned.

That’s because to do so would be to concede something next to impossible for modern liberals: If you are serious about reducing crime, the way to do it is to find smarter and better ways to go after bad guys, especially the ones carrying guns.

As for the squeegee men, they were targeted in the Giuliani years under a “broken windows” theory of policing, which held that the way to restore order and rein in the big crime was by not turning a blind eye to the smaller things. Giuliani also introduced a computer crime-tracking system, CompStat, and began holding commanders accountable for their precincts.

Bloomberg took up where Rudy left off — and with Commissioner Kelly in charge has driven violent crime down further than most people thought possible. Most notably, the cops stopped suspicious characters and, if need be, frisked them.

We do not believe our city is on the brink of ruin. We do believe that many people either do not remember how bad it was before — or take for granted the achievements. The result is this craziness: New York’s police force has become the main target for attack by the leading candidate for mayor at a time when the NYPD has given us the safest big city in America.

We recommend people take a look at cities like Chicago or Detroit for a good reminder that there’s nothing inevitable about a safe city. We further hope they take a close look at how police do their jobs in these cities.

That’s because in all too many other parts of modern urban America, whole neighborhoods — usually poor or minority or both — are simply written off to the hoodlums as cops concentrate on the better, more well-heeled neighborhoods.

That’s what’s at stake in this election. Back in the days when more than six people a day were killed in New York, versus about one a day today, even the Times worried that New Yorkers “think twice about where they can safely walk.” The city felt like “a New Beirut.”

We hope New York will never slip back to the bad old days. Which is why we’d like to see more appreciation for the achievement the cops have given us — and the risk that comes from second-guessing it.